(navigation image)
Home American Libraries | Canadian Libraries | Universal Library | Community Texts | Project Gutenberg | Children's Library | Biodiversity Heritage Library | Additional Collections
Search: Advanced Search
Anonymous User (login or join us)
Upload
See other formats

Full text of "Electron Tubes In World War II"

1947 



PROCEEDINGS OF THE I.R.E.— Waves and Electrons Section 



295 



Electron Tubes in World War II" 

JOHN E. GORHAMf, member, i.r.e. 



Summary — Although the military uses of electronics have been 
well publicized in technical journals, the improvements in electron 
tubes that made possible these military innovations have not been 
fully reported. While this information is known in some detail by 
the technical people who were engaged in various phases of tube 
research and development, an over-all summary of the work done 
by industrial laboratories and Federal agencies has not been availa- 
ble to many engineers and students interested in this field. In this 
paper, the status of electron-tube development at the close of the 
war is indicated in broad outline; a more comprehensive picture de- 
pends upon more detailed reports from the various laboratories en- 
gaged in war activities. 

This summary of wartime advances in electron tubes is based on 
the knowledge of the vacuum-tube field gained by the engineers of the 
thermionics branch of the Signal Corps Engineering Laboratories, 
Bradley Beach, New Jersey, in developing, standardizing, and giving 
type approval of all tubes procured for the army during the war. 

No effort is made to give specific credit either to individuals or 
industrial organizations. By and large it is a story of common achieve- 
ment of many people, with industry working hand in hand with the 
War and Navy Departments to meet the urgent requirements of an 
ever-expanding demand for new and improved military electronic 
equipment. 



I. General Research and Miscellaneous 
Related Tube Problems 

Cathodes 

AT THE start of World War II it was the practice 
/-^\ to use oxide cathodes in low-power and receiv- 
ing-type tubes, thoriated-tungsten filaments in 
medium-power tubes, and pure tungsten in high-power 
tubes. In general there were few power-pulse require- 
ments. During the war, the use of thoriated filaments 
had been successfully extended to all types of power 
tubes, including the highest- power pulsed-oscillator- 
tubes designed. In addition, during the last year of the 
war, oxide cathodes were used in power tubes capable of 
delivering 500 or 600 kilowatts peak power, and up to 
several megawatts peak power in magnetrons. The peak 
emission of thoriated filaments, for design purposes, has 
been increased from approximately 100 milliamperes 
per watt to approximately 200 milliamperes per watt. 
The peak emission from oxide cathodes has been in- 
creased to 30 amperes per square centimeter in produc- 
tion tubes, and as high as 80 amperes per square 
centimeter for several hundred hours in laboratory 
tubes. The highest peak emission reported is about 140 
amperes per square centimeter. Oxide-cathode direct- 
current emission has been increased to approximately 
0.S ampere per square centimeter under optimum con- 
ditions. 



* Decimal classification: R330. Original manuscript received by 
the Institute, March 27, 1946; revised manuscript received, July 31, 
1946. 

t Evans Signal Laboratory, Belmar, New Jersey. 



There was little advance in the efficiency and stability 
of secondary-electron multipliers during the war. Elec- 
tron multipliers may be considered to have a nominal 
multiplication factor of approximately 5 per stage for 
optimum acceleration voltages of the order of a few 
hundred volts per stage. After about 200 or 300 hours 
the performance of these multipliers is seriously reduced. 

Except for low-power voltage-regulator and mercury- 
pool type tubes, relatively few tubes having cold cath- 
odes were used in military equipment during World 
War II because of the lack of satisfactory life from such 
cathodes. In one type of pulse-modulator tubes, mercury 
is held in fine iron powder to permit use in aircraft. 
Mercury-pool ignitrons were used as pulsed modulator 
tubes to a limited extent. 

It has been generally proved that at least 80 per cent 
of the total emission from the magnetron cathode is 
largely due to electrons emitted as a result of back- 
bombardment by electrons that do not reach the anode. 
As a result of such back-bombardment, considerable 
power is sent back to the cathode, with resultant heating 
and evaporation of the cathode coating and even the 
base metal. This has been overcome to some extent by 
appropriate reduction in power after the magnetron 
reaches stable operation. Some higher-frequency mag- 
netron cathodes actually have radiators. More rugged 
types of coatings have been developed in which the 
oxides are pressed into a wire mesh which is sintered to 
a base cylinder, or in which approximately 50 per cent 
of the coating consists of 3- or 4-micron nickel powder to 
increase electron and heat conductivity and also to in- 
crease to some extent the binding force holding the 
barium. 

Grids 

An outstanding advancement during World War II 
has been the development of alloys and surfaces which 
overcome the problem of primary grid emission in thori- 
ated-filament tubes, thereby eliminating the phenome- 
non of grid blocking, which normally leads to destruc- 
tion of such tubes. These alloys include 4 per cent 
tungsten-platinum alloy wire, platinum-coated molyb- 
denum-core grid wire, and "mossy"-surfaced tantalum 
or molybdenum wire. 

It has been found that the presence of secondary 
emissipn tends to reduce the driving power of conven- 
tional grid tubes. The uniformity and stability of such 
secondary emission are very poor, however, and the cur- 
rent practice is generally to avoid making use of this 
factor in service tubes. 

It has been discovered that there are certain tempera 
tures at which the emission from grid wires is a mini 
mum, and though it is not generally possible to maintain 



296 



PROCEEDINGS OF THE I.R.E.— Waves and Electrons Section 



March 



the grids at this temperature, at least one tube type has 
been put into wide production with a fair degree of suc- 
cess using this principle. A second method used in re- 
ceiving tubes (and, during the last years of the war, in 
power tubes) consists of the use of heat conduction to 
maintain grid temperature sufficiently low to minimize 
the effect of emission. This has been accomplished in 
some cases, such as in the 7C22, by the use of nickel 
cylinders with grid straps punched and rotated 90 de- 
grees to reduce their effective cross section to electron 
flow but at the same time maintain their cross section 
for heat flow. 

In various other power receiving tubes relatively 
large copper rods have been fastened at appropriate 
intervals to help remove heat. Another application 
makes use of very short grid wires to facilitate conduc- 
tion to end rings. Still another method employed with 
moderate success in reducing grid emission involves the 
use of gold-plated molybdenum wire. It has been found 
that the gold will dissolve barium for at least 1000 hours 
in tubes such as the 715C. A solid solution is ultimately 
formed which apparently draws together and exposes 
the base metal through the resultant cracks. 

Anodes 

During World War II the problem of anode heat dis- 
sipation had not been a major one, except in planar-type 
lighthouse tubes. A principal problem in connection 
with anode design, and for that matter with general 
design of tubes, has been to reduce lead-reactance effects 
by providing extremely low-impedance paths at radio- 
frequency connections. The most important advance in 
anode design has been the development of various differ- 
ent but essentially similar re-entrant anode designs. 
These employ large-diameter glass-to-metal seals in 
both copper and kovar, and result in attendant reduc- 
tion of lead -reactance effects up to at least 700 mega- 
cycles. 

Zirconium or zirconium compounds have been sprayed 
on anodes to make them more nearly perfect black-body 
radiators, and simultaneously serve as getters. The prin- 
cipal requirement in planar-tube anode design at present 
is to improve heat dissipation and frequency drift due 
to warm-up. 

Gas Reservoirs 

Titanium-hydride reservoirs have been developed 
which are capable of maintaining the pressure at con- 
stant value and appreciably extending the life of hydro- 
gen thyratrons under extreme operating conditions. 

II. Magnetron Tubes 

The development of the magnetron as an efficient 
microwave generator took place almost entirely during 
World War II. During the war, the magnetron advanced 
from the status of the elementary split-anode variety to 



the highly perfected and complex multiresonant-cavity 
type. Operating efficiencies were raised from about 10 
to over 50 per cent. Tubes were developed and produced 
in large numbers for wavelengths as short as approxi- 
mately 1 centimeter. Representative types of mag- 
netrons are shown in Fig. 1. 




IIP 

m 




Fig. 1 — Representative types of magnetrons: (a) 2J31 hole-and-slot 
pulse type, (b) 2J54 tunable pulse type, (c) 2 J 64 vane type for 
pulse communication, (d) 5J31 split-anode continuous-wave type, 
(e) 3J21 rising-sun pulse type. 

During the course of the war, extensive studies were 
made of mode separation and the manner and efficiency 
of operation. Methods of eliminating undesirable modes 
(arising from multiple degeneracy due to the multireso- 
nator anode blocks) were developed, such as strapping 
and the use of "rising-sun" alternately long and short 
cavity construction. The usual technique of strapping 
consists of electrically connecting alternate cavity vanes 
near the cathode ends by means of metal straps or wires 
within the tube. This strapping depends on end effects 
at the top and bottom of the vanes. The rising-sun anode 
construction consists of making alternate cavities tuned 
respectively to frequencies above and below the operat- 
ing frequency of the magnetron, and was originated to 
avoid straps in super-high-frequency tubes. Lately, the 
fact that the rising-sun structure does not depend on end 
effects has been used in designing higher-power, longer- 
anode magnetrons. 

Several mechanical tuning methods were developed. 
These include internal tuning by means of moving 
plungers in the resonant cavities ("crown of thorns"), 
changing the capacitance of the straps to ground and 
each other, the addition of an external tunable resonator 
coupled to an internal resonator or strap, and simultane- 
ous application of strap and plunger tuning. 

"Packaging" was also introduced, whereby the 



1947 



Gorham: Electron Tubes in World War II 



297 



magnetron was produced as a complete unit containing 
or having attached permanent magnets as an integral 
part of the magnetron instead of depending on the fur- 
nishing of proper magnetic fields as part of the operating 
equipment. 

At present, several 25-centimeter pulsed magnetrons 
of fixed frequency are available with peak powers as 
high as 1 megawatt. Development has just been com- 
pleted on a tunable type capable of 600 kilowatts peak 
power output and 8 per cent tuning range. 

At wavelengths of about 10 centimeters, tubes have 
been produced in quantity with peak powers ranging up 
to approximately 2 megawatts. Tunable tubes have been 
made which have approximately 7 per cent tuning range 
and 1 megawatt peak power output. 

The maximum peak power attainable at about 3 centi- 
meters is approximately 1 megawatt from a fixed- 
frequency magnetron. A variable-frequency magnetron 
is also available at this frequency capable of 50 kilo- 
watts peak power and 12 per cent tuning range. At 
about 1 centimeter only two fixed-frequency pulse mag- 
netron types have been produced in quantity. The tubes 
are capable of peak powers of the order of 50 kilowatts. 
In general, the life expectancy of pulsed magnetrons is 
in the neighborhood of 500 hours, except at extremely 
short wavelengths where life expectancy is about 250 
hours. 

Continuous-wave magnetrons using split anodes in 
the high- and ultra-high-frequency bands, and cavities 
in the higher frequency bands, have been developed pri- 
marily as sources of jamming power of from over 1 
kilowatt down to about 50 watts. Due to serious back- 
bombardment of the cathodes, tube life is usually less 
than 100 hours, although efficiencies are about 40 per 
cent. Interdigitated magnetrons, having as anodes two 
cylindrical sets of interlocking teeth, have been made 
to give about 15 watts output at 7 centimeters. 

During the last part of the war, magnetron modula- 



tion was investigated to permit communication at 
all frequencies. One electronic frequency-modulation 
method consists of varying the current of an electron 
beam through one of the magnetron cavities. This 
method has been used at 4000 megacycles to get 4 mega- 
cycles total swing at about 25 watts continuous-wave 
power output. Preliminary tests show that external 
magnetrons may be used to modulate the magnetron 
generator tube by virtue of change of electronic react- 
ance, but at present modulation linearity is not as good 
as that obtained by the former method. Amplitude mod- 
ulation is not satisfactory at this date, but there are 
indications that considerable success may be achieved in 
the near future. Pulse-time modulation is feasible at any 
frequency and involves transmission at constant power 
level. 

III. Transmit-Receive Tubes 

The transmit-receive (TR) tube (Fig. 2) is a switching 
tube, usually gas-filled, which is generally used in radio- 
frequency systems (radar, for example) where a trans- 
mitter and receiver make use of a common antenna. Its 
function is to protect the receiver input-circuit elements 



.;.« 


'*■ 


pi 










Fig. 2 — Transmit-receive tubes; types 721 A, 1B37. 

during the pulsing of the transmitter and allow the 
radio-frequency power received by the antenna between 
pulses to reach the receiver. Antitransmit-receive (ATR) 
tubes are used in conjunction with TR tubes to reduce 
the dissipation of receiver signals in the transmitter. 



Table I 
TR-Tube Performance Characteristics 



Type 


Application 


Wavelength 


Power level 


Insertion loss 


Recovery time 


Bandwidth 


1B23 


TR 


20-50 centimeters 


50 kilowatts 


1 decibel 


— 


highQ 


702A, B 


TR 


20-50 centimeters 


50 kilowatts 


— 


— 


— 


721B 


TR external cavity 


10 centimeters 


250 kilowatts 


1.0-1.5 decibels 


<7 microseconds 


high Q 


1B27 


TR external cavity 


10 centimeters 


250 kilowatts 


1.0-1.5 decibels 


<5 microseconds 


high Q 


1B58 


TR fixed- tuned 


8-11 centimeters 


200 kilowatts 


1.0-1.5 decibels 


15 microseconds 


10 per cent 


1B55 


TR fixed -tuned 


8-11 centimeters 


200 kilowatts 


1.0-1.5 decibels 


15 microseconds 


10 per cent 


PS3S 


TR fixed-tuned 


8-11 centimeters 


200 kilowatts 


1.0-1.5 decibels 


15 microseconds 


10 per cent 


1B44 


ATR fixed- tuned 


8-11 centimeters 


1 milliwatts 


1 decibel 


■ — 


5 per cent 


1B52 


ATR fixed-tuned 


8—1 1 centimeters 


1 milliwatts 


1 decibel 


— 


5 per cent 


1B53 


ATR fixed-tuned 


8-11 centimeters 


1 milliwatt 


1 decibel 


— 


5 per cent 


1B56 


ATR fixed- tuned 


8-11 centimeters 


1 milliwatt 


1 decibel 


— 


5 per cent 


1B57 


ATR fixed -tuned 


8-11 centimeters 


1 milliwatt 


1 decibel 


- — 


5 per cent 


1B38 


Pre-TR for use with low- 
power TR 


10.7 centimeters 


1 milliwatt 


0.10 decibel 


20 microseconds 




1BS4 


Pre-TR for use with low- 
power TR 
TR tunable self-contained 


8.4 centimeters 


1 milliwatt 


0.10 decibel 


20 microseconds 


— 


1B24 


3 centimeters 


60 kilowatts 


1.0-1.5 decibels 


<3 microseconds 


high Q 


724B 


cavity 
TR external cavity 


3 centimeters 


60 kilowatts 


1.0-1.5 decibel 


<6 microseconds 


high Q 


1B63 


TR broad -band fixed- tuned 


3 centimeters 


300 kilowatts 


<0. 8 decibel 


<5 microseconds 


12 per cent 


1B35 


ATR fixed- tuned cavity 


3 centimeters 


60 kilowatts 


0.8 decibel ' 


— 


6 per cent 


1B37 


ATR fixed-tuned cavity 


3 centimeters 


60 kilowatts 


0.8 decibel 


— 


6 per cent 


1B26 


TR self-contained cavity 


1 centimeter 


40 kilowatts 


0.85-1.5 decibels 


<4 microseconds 


highQ 


1B36 


ATR fixed-tuned 


1 centimeter 


40 kilowatts 


0.8 decibel 


— 


>2 per cent 



298 



PROCEEDINGS OF THE l.R.E— Waves and Electrons Section 



Marc, 



Pre-TR tubes are used for added receiver protection 
during transmitter pulses. These last two tube types 
have general requirements similar to that of TR tubes 
(see Table 1). TR, ATR, and pre-TR tubes should have 
low leakage power to the receiver during the transmitter 
pulse, rapid recovery time immediately following the 
pulse to enable the maximum received energy to reach 
the receiver for short range echoes, and satisfactory life. 
Most tubes were filled either with argon or mixtures of 
hydrogen and water vapor at pressures in the range of 
10 to 25 millimeters. 

In general, the recovery time of good tubes at power 
levels of 30 kilowatts peak is in the order of 4 to 7 micro- 
seconds. At higher powers, recovery-time figures are 
progressively larger. For instance, at line powers of 100 
kilowatts the recovery time is approximately 50 per cent 
greater than at 30 kilowatts. As might be expected, 
leakage power is also a function of line power. At 30 and 
100 kilowatts the leakage powers are of the order of 20 
and 75 milliwatts peak, respectively. The insertion loss 
is approximately one decibel. Recently multicavity 
fixed-tuned tubes have been made with a frequency 
coverage of about 12 per cent. 

IV. Crystal Rectifiers 

Crystal rectifiers (Fig. 3) are used in receiver applica- 
tions for mixers, video detectors, second detectors, and 
direct-current restorers. In construction they consist of 
a semi-conductor, either silicon or germanium, in con- 
tact with a cat's whisker of metal, usually tungsten. At 
present, crystal mixers give the lowest noise figures in 
receivers above about 1000 megacycles. 



intermediate-frequency amplifier of 5 decibels noise 
figure, receiver noise figures are attainable which vary 
from about 12.7 decibels at 3000 megacycles to 15.2 
decibels at 30,000 megacycles. 

Germanium crystals, used as second detectors, at 
present are capable of withstanding 50 or more volts in 
the back direction, compared with about 5 volts for 
silicon crystals. In general, they have rectification effi- 
ciencies in the same order of magnitude as receiving-type 
diode tubes. For direct-current restorer applications, 
germanium crystals have resistances, measured at 1 volt, 
greater than 0.1 megohm in the back direction and ap- 
proximately 200 ohms in the forward direction. Ger- 
manium crystals are being used at present as second 
detectors and direct-current restorers for experimental 
circuit work. Their properties, especially as compared to 
diodes, are being studied. 

V. Klystrons 

Development and application of klystrons during 
World War II has mainly centered about reflex tubes for 
local-oscillator use, requiring about 20 milliwatts of 
power output, and signal-generator use, requiring about 
one watt. Although the theoretical maximum efficiencies 
are 30 per cent for the reflex klystron and 58 per cent for 
the two-cavity type, the actual efficiencies thus far at- 
tained are only a few per cent for reflex tubes and 5 to 
6 per cent for two-cavity types. The best tube in this 
respect, to date, is the 2K54 for which efficiencies of 
10 per cent are obtained under pulsed operating con- 
ditions. 




Fig. 3— Crystal detector: 1N21. 

In general, microwave crystal converters have conver- 
sion losses of the order of about 6.5 to 8.5 decibels, being 
best at 3000 megacycles and worst at about 30,000 
megacycles. They are capable of withstanding pulses 
ranging from 5 ergs at 3000 megacycles to 0.1 erg at 
30,000 megacycles. On the basis of their use with an 






Fig 4— Thermally tuned reflex klystron, 9000 megacycles: 
type 2K45. 



Tuning of klystrons is generally accomplished by 
either changing the resonant frequency of the cavity or, 
in the case of reflex klystrons, by varying the potential 
of the repeller. Repeller-voltage changes are capable of 
producing only relatively small frequency changes of the 



1947 



Gotham: Electron Tubes in World War II 



299 



order of 1 per cent. The degree of frequency change at- 
tainable by means of cavity variation depends largely 
on the cavity construction. Klystrons designed to oper- 
ate with external cavities may have frequency tuning 
ranges in the order of 2 to 1. Klystrons constructed with 
cavities which are an integral part of the tube usually 
are tuned by the motion of a metal diaphragm, which 
permits variation in the spacing of the resonator grids. 
This produces changes in grid-to-grid capacitance and 
consequent shift in the resonant frequency. 

Tuning has also been accomplished in some tube types 
by electronic control of an auxiliary electron source 
within the same envelope, which heats a thermally 
sensitive mechanical element attached to the cavity dia- 
phragm. The thermal time constant of such devices 
varies between 2 and 10 seconds, depending on the type 
of tube. Tubes with thermal tuning are available in the 
regions of 10,000 and 25,000 megacycles (Fig. 4). 

The power output of reflex klystrons below 3000 
megacycles is of the order of 1 watt. Between 3000 
and 10,000 megacycles, \ watt may be attained. Above 
10,000 megacycles, available types exist only in the re- 
gion of about 25,000 megacycles and are capable of 
approximately 20 milliwatts output. Two-cavity kly- 
strons have been produced in the 2300- to 4000-mega- 
cycle region, capable of delivering between 20 and 40 
watts of power. 

VI. Planar Tubes 

Planar-type tubes (Fig. 5) are suitable for high-fre- 
quency operation because of (a) reduction in lead in- 
ductances by use of disk seals, (b) reduction in inter- 
electrode capacitances by means of small electrode areas 





and parallel-plane structure, and (c) essentially complete 
enclosure of the radio-frequency fields permitted by a 
tube construction suitable for operation in an inclosed 
cavity. A number of types, all developed during World 
War II, are now available. These include the 2C40, a 
low-power triode with 50 milliwatts output at 3370 
megacycles; 2C43, a pulse triode with 750 watts peak 




Fig. 5 — Cutaway planar tubes: types 2C43, 3C22. 



Fig. 6 — Cathode-ray-tube screen test. 

output at 3370 megacycles; 3C22, a continuous-wave 
triode with 25 watts output at 1400 megacycles; 2C38, 
continuous-wave triode with 10 watts output at 2500 
megacycles; and the 2C36 and SB846A, British-type 
disk-seal triodes for low-power use up to about 4000 
megacycles. 

Present types of planar tubes are constructed with 
oxide-coated cathodes; tungsten or nickel grids; and 
steel, molybdenum, or kovar paltes. The glass seals are 
made to silver-plated steel or kovar. In the case of sil- 
ver-plated steel, special glass having a thermal-expan- 
sion coefficient equal to steel is used. Interelectrode 
spacings on the 2C40 type are as low as 0.003 inch and 
0.010 inch for grid to cathode and grid to plate, respec- 
tively. These small spacings, in view of the fact that such 
tubes are intended for use in accurately machined cavi- 
ties, require unusually small mechanical tolerances in 
manufacture. 

VII. Indicator and Pickup Tubes 

Cathode-ray indicator tubes are used wherever a visi- 
ble indication of rapidly changing electrical phenomena 
is required. Because of the almost infinitesimal inertia 
of the electron beam, these tubes are capable of re- 
sponses far more rapid than any mechanical indicators. 



300 



PROCEEDINGS OF THE I.R.E— Waves and Electrons Section 



March 



The transforming of visible or invisible radiation 
images into electrical signals is accomplished in elec- 
tronic pickup tubes. Such tubes are designed to have 
high sensitivity to radiation. By means of very rapid 
electronic scanning of a photosensitive mosaic, high- 
resolution electrical transmission of rapidly moving 
images is accomplished. 

During the war, the following improvements were 
made in electron guns: 

(a) In electrostatic-focus types, zero first-anode-cur- 
rent guns were developed in which the first anode did 
not intercept any beam current, with the result that 
power-supply requirements were reduced and better fo- 
cusing control was obtained. 

(b) In magnetic-focus types an additional cylinder 
was added to the high- voltage anode, which aided in 
alignment of the gun and improved the focus. 

(c) Limiting apertures were added in magnetic-focus 
types to reduce the spot size and improve the focus. 

With regard to screens, several new types were de- 
veloped : 

(a) Double-layer screens which have the property of 
emitting increased intensities of persistent light after 
successive excitations of the screen. The color of its 
fluorescent light is different from that of its phosphores- 
cent light. 

(b) Dark-trace screens showing a darkening of the 
normally white screen material, usually potassium 
chloride, at the point of excitation by tt^§ electron 
beam, were used in projection systems. 

(c) Exponential screens having light output which 
decays at such rate that its instantaneous intensity is 
proportional to exponential t/t , where t is a constant of 
the screen and t is the time. 

Commutator tubes of several varieties were developed 
during the war for multichannel communication over a 
single transmission frequency. 

Improved tubes suitable for projection purposes were 
also developed during the war with high light output 



(6 candle power per watt) and good contrast. Cathode- 
ray tubes with two or more guns in the same envelope 
were developed for special applications, eliminating 
complex switching circuits. Pickup tubes were developed 
with sensitivities in the infrared. Tubes were also de- 
veloped capable of converting infrared images directly 
to visible images by focusing the electron pattern from 
a photosensitive surface on a fluorescent screen at the 
opposite end of a cylindrical tube. 

At present, cathode-ray tubes with faces from 1 to 
12 inches in diameter are available in quantity. These 
tubes are in some instances focused and deflected by 
electrostatic methods and in others by magnetic meth- 
ods. 

The various screen types and general information con- 
cerning their properties are listed in Table II. 

Levels of fluorescent light output vary according to 
screen types, being about 15 foot-lamberts for tubes of 
the highest output (nonprojection tubes with PI 
screens). Improvements in focusing and line widths 
were limited and were less than a factor of 2 to 1. Pres- 
ent line widths of from 0.3 millimeter to 1 millimeter 
are a function of tube size and gun construction (Fig. 6). 

Pickup tubes of the orthicon type have been produced 
with sensitivity in the infrared and in the blue part of 
the spectrum. Orthicon tubes have been made with a 
resolution of 1500 lines per frame at the center for high 
resolution reconnaissance work. For portable systems, 
tubes have been constructed operating with only a few 
hundred volts having a sensitivity of 0.03 microamperes 
per foot-candle. 

VIII. Power and Gas Tubes 

At the start of World War II radar transmitters were 
operated at or below about 200 megacycles and used 
tubes which had thoriated filaments. During the war 
oxide cathodes came to be used in power-oscillator tubes 
with a reduction of cathode power by a factor of about 
five. 



Table II 
Cathode-Ray-Tube Screen Characteristics 



Screen 
type 



Composition 



Color 



Persistence 



Decay time to 
1 per cent (seconds) 



Applications 



P5 


C a W0 4 :(W) 


Blue 


short 


10" 5 


Pll 


a* — Zns : Ag 


Blue 


short 


0.005 


P4 


a* — ZnsiAg 

+ 
Zn 8 BeSi 5 0i 9 :Mn 


White 


short 


0.005+0.06 

(B) (Y) 


PI 


Zn 2 Si0 4 :Mn 

(a) 
Zn(Mg)F 2 :Mn 


Green 


short 


0.05 


P12 


Orange 


long 


0.4 


P2 


ZnS:Cu(Ag) 

(0*) 
0*— ZnS:Ag 


Green 


long 


0.3 


P14 


White 


long 


1 




on 


i 








ZnS(75):CdS:Cu 


Orange 






P7, (P8) 


/3*— Z|nS:Ag 

on 
ZnS(86):CdS:Cu 


White 

1 
Yellow- 


long 


3 


P10 


KC1 


Magenta on White 


long 


5 



Photography of rapid transients (to 60 kilocycles) . 
Photography of transients (to 9 kilocycles). 
Television. 



Most cathode-ray oscilloscopes. Rapid-scan ra- 
dar cathode-ray tube. 

Fire-control radars operating at 4 to 16 scans per 
second. 

Prewar long-persistence oscilloscopes. 

Eagle and H2K radars operating at about 1 
scan per second. 

Most radars operating slower than 1 scan per 
second. 

Radars operating in high ambient light and 
slower than 0.2 scan per second. 



1947 



Gorham: Electron Tubes in World War II 



301 



Several types of \- to J-megawatt triode tubes have 
been developed with the tuned circuits inside the vac- 
uum envelope. By the close of the war, triode oscillator 
tubes had been developed which gave approximately 
0.6 megawatt up to about 700 megacycles. Power-am- 
plifier tubes are available that can handle 100 or 200 
watts continuous-wave output up to 700 megacycles 
with a power gain of about 5 decibels. 

Hydrogen thyratrons were originated and put into 
production during the war to eliminate temperature de- 
pendence of mercury tubes. These thyratrons handle 
powers of from a fraction of a watt to 2 megawatts pulse 
power. Series and/or parallel operation of thyratrons 




Fig. 7- 



-Pulse modulator tubes: 5C22 hydrogen thyratron ; 715C high- 
vacuum type; 1R21 mercury-pool ignitron. 



has been accomplished to allow up to four times the 
power of a single thyratron. Ignitrons have been used up 
to 2 megawatts at 20 microseconds pulse width. High- 
vacuum modulator tubes have been developed to handle 
a few hundred kilowatts peak power at duty ratios of 
about 0.0006. Tubes of each of these types are shown in 
Fig. 7. 

The resnatron, employed during the war in radar 
countermeasures to jam German radar, is the most 
powerful ultra-high-frequency oscillator and amplifier 
now in existence. It supplies over 50 kilowatts in con- 
tinuous-wave operation at frequencies ranging from 350 
to 650 megacycles, with a plate efficiency of the order of 
60 to 70 per cent. Features of this tetrode include beam- 
forming grids, electron bunching, and self-contained 
resonant cavities which permit phase-shift compensation 
for transit-time effects without lowering efficiency. 

IX. Receiving Tubes 

There are so many types of receiving tubes that it is 
impossible to begin to describe them here. Consequently 
only a few practices of a general nature that came into 
considerably wider employment during the war will be 



mentioned in this section. The use of standard tubes at 
low plate and screen voltages was accomplished to allow 
operation directly from a 24-voIt storage battery in 
place of a high-voltage power supply. Subsequently, 
tubes with 26.5-volt filaments and a design optimized 
for 28- volt plate and screen operation were developed. 
Tubes were "ruggedized" to withstand vibration and 
shock up to 500 times the acceleration of gravity. Sub- 
miniature tubes (T-3 bulbs of f-inch diameter) were in 
existence before the war for hearing-aid use. During the 
war, subminiature types for VT fuzes were developed 
which could withstand being shot from guns. Size and 
weight limitations of new radar and allied equipment, 
along with the need for high peak power output, created 
the need for receiving-type tubes capable of operating 
in a pulsed condition at potentials and currents far 
above their rated values. Fig. 8 shows six different types 
of receiving tubes. 









f 



M 



Fig. 8 — Receiving tubes having transconductances of 3000 to 5000: 
G, GT, metal, lockin, miniature, and subminiature tube types 
6J5G, 6J5GT, 6J5, 7F8, 6J6, 6K4. 

There is now an overabundance of j-eceiving-tube 
types — one or two thousand, or perhaps more. It is not 
unusual to find half a dozen or more tubes, substan- 
tially equivalent, differing by having several filament 
voltages, two or three types of bases and bulbs, and 
different arrangements of pin connections. Almost every 
metal-tube type is duplicated in a glass version with the 
same base, and most are also duplicated in lock-in con- 
struction under different type designations. Now most 
of these types are becoming available in miniature bulbs. 

X. Acknowledgment 

It is a pleasure to acknowledge the aid of my associ- 
ates in the preparation of this paper: M. E. Crost, 
K. Garoff, D. R. Gibbons, L. L. Kaplan, B. Kazan, 
H. L. Ownes, D. E. Ricker, and C. S. Robinson, Jr.